From summer heat less than 10 days ago to snow and cold now over eastern Europe! What a flip from September’s warmth to October’s cold so far. Where it’s been warmest in Sept, it’s coolest so far in Oct. That’s the way it goes!

September anomaly

October so far

The same drivers which do one thing at one time of year do another at another time of year. Remember the Russian heat wave back in 2010? The winter of 2011-12 was one of the worst for the same region. A rubber band effect?

The negative NAO pattern is persistent but we’re seeing a different pattern now thanks to the seasonal shift.

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In the past week, there’s been considerable growth in the all important Eurasian snow cover, the key driver in the initial development and depending upon amount of snow cover, the intensity and reach of the Siberian high. Other global drivers including distant ENSO, AO decides whether it’s a cold or mild winter for the mid-latitudes where as players such as PNA and NAO determine WHERE where the cold positions itself during winter.

Europe is turning colder thanks to the combination of increasing Eurasian snow cover, and the transportation source of a large blocking high over Scandinavia which is pulling increasingly cold Siberian air westward providing the first snowfall and severe frosts initially to Russia and now into Ukraine, Poland and could reach Germany today. The strong east wind is even causing a nip over what’s been a mild UK, particularly along east facing coasts.

Though snow is falling, it will struggle to stick due to the still warm ground. That’s despite some very cold nights.

This was Sat AM.

Notice the cold is stronger and extends further west by Sun AM.

Just a week ago, cities such as Warsaw, Kiev, Moscow and Tallinn where enjoying mid to upper 20s so the ground takes time to cool.

Quick and widespread snowpack growth does have atmospheric implications for both near and long term weather. It often tends to build the NH cold pool faster, stronger and more widespread but interestingly it’s been linked to more of a negative Arctic Oscillation winter.

This fast growth of snow cover is one thing but perhaps a more eye-catching aspect to watch is the behaviour of the polar stratosphere which has been weak over Asia and the Pacific but stronger over Greenland and Europe over the past 2 winters, why? I would put it down to the warm waters over the North Pacific combined with solar maximum.

Warming of waters around Greenland and off Norway and slight cooling now within the Gulf of Alaska suggests a more uniform positive height field this winter and would be the first since probably 2013. When looking at the polar vortex, well it’s weak at 50mb. The last two Octobers have seen a stronger and more pole positioned vortex.

The past two winters have seen a weak Aleutian low and when this is the case, the Icelandic low tends to be stronger but the current setup and model projections are hinting at the opposite this winter.

The solar cycle though not back into a minimum state for another 3-5 years, is however well off the maximum and around the midway point. These ‘in between years’ are tricky and one needs to watch the ocean and the seasonal variability in warming and cooling as well as the El Nino and other drivers.

The cool pattern looks to hold through much of the rest of October across Europe as the NAO/AO looks to remain negative.

The below GFS ensemble shows a dry, cool pattern for UK and West Europe with the mean ridge remaining anchored across the north then more towards Iceland. Note the persistency in positive over negative.

2m temp anomaly

 

See this morning’s video for the discussion.

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